1Hyper-V network driver
2======================
3
4Compatibility
5=============
6
7This driver is compatible with Windows Server 2012 R2, 2016 and
8Windows 10.
9
10Features
11========
12
13  Checksum offload
14  ----------------
15  The netvsc driver supports checksum offload as long as the
16  Hyper-V host version does. Windows Server 2016 and Azure
17  support checksum offload for TCP and UDP for both IPv4 and
18  IPv6. Windows Server 2012 only supports checksum offload for TCP.
19
20  Receive Side Scaling
21  --------------------
22  Hyper-V supports receive side scaling. For TCP & UDP, packets can
23  be distributed among available queues based on IP address and port
24  number.
25
26  For TCP & UDP, we can switch hash level between L3 and L4 by ethtool
27  command. TCP/UDP over IPv4 and v6 can be set differently. The default
28  hash level is L4. We currently only allow switching TX hash level
29  from within the guests.
30
31  On Azure, fragmented UDP packets have high loss rate with L4
32  hashing. Using L3 hashing is recommended in this case.
33
34  For example, for UDP over IPv4 on eth0:
35  To include UDP port numbers in hashing:
36        ethtool -N eth0 rx-flow-hash udp4 sdfn
37  To exclude UDP port numbers in hashing:
38        ethtool -N eth0 rx-flow-hash udp4 sd
39  To show UDP hash level:
40        ethtool -n eth0 rx-flow-hash udp4
41
42  Generic Receive Offload, aka GRO
43  --------------------------------
44  The driver supports GRO and it is enabled by default. GRO coalesces
45  like packets and significantly reduces CPU usage under heavy Rx
46  load.
47
48  Large Receive Offload (LRO), or Receive Side Coalescing (RSC)
49  -------------------------------------------------------------
50  The driver supports LRO/RSC in the vSwitch feature. It reduces the per packet
51  processing overhead by coalescing multiple TCP segments when possible. The
52  feature is enabled by default on VMs running on Windows Server 2019 and
53  later. It may be changed by ethtool command:
54	ethtool -K eth0 lro on
55	ethtool -K eth0 lro off
56
57  SR-IOV support
58  --------------
59  Hyper-V supports SR-IOV as a hardware acceleration option. If SR-IOV
60  is enabled in both the vSwitch and the guest configuration, then the
61  Virtual Function (VF) device is passed to the guest as a PCI
62  device. In this case, both a synthetic (netvsc) and VF device are
63  visible in the guest OS and both NIC's have the same MAC address.
64
65  The VF is enslaved by netvsc device.  The netvsc driver will transparently
66  switch the data path to the VF when it is available and up.
67  Network state (addresses, firewall, etc) should be applied only to the
68  netvsc device; the slave device should not be accessed directly in
69  most cases.  The exceptions are if some special queue discipline or
70  flow direction is desired, these should be applied directly to the
71  VF slave device.
72
73  Receive Buffer
74  --------------
75  Packets are received into a receive area which is created when device
76  is probed. The receive area is broken into MTU sized chunks and each may
77  contain one or more packets. The number of receive sections may be changed
78  via ethtool Rx ring parameters.
79
80  There is a similar send buffer which is used to aggregate packets for sending.
81  The send area is broken into chunks of 6144 bytes, each of section may
82  contain one or more packets. The send buffer is an optimization, the driver
83  will use slower method to handle very large packets or if the send buffer
84  area is exhausted.
85